Fuel injected engines employ fuel injectors, each of which delivers a metered quantity of fuel to an associated engine cylinder during each engine cycle. Prior fuel injectors were of the mechanically or hydraulically actuated type with either mechanical or hydraulic control of fuel delivery. More recently, electronically controlled fuel injectors have been developed. In the case of a mechanically actuated electronic unit injector, fuel is supplied to the injector by a transfer pump. The injector includes a plunger which is movable by a cam-driven rocker arm to compress the fuel delivered by the transfer pump to a high pressure. An electrically operated mechanism either carried outside the injector body or disposed within the injector proper is then actuated to cause fuel delivery to the associated engine cylinder.
In prior fuel injector designs, high pressure fuel is conducted through passages which are located outside of a central recess containing a solenoid which operates a valving mechanism. The passages are located close to the outer surface of the fuel injector and are formed by drilling intersecting holes. After drilling, portions of some of the holes must be filled with plugs. These passages and plugs are subjected to very high fluid pressures, thus requiring careful design and increasing complexity and cost.
In addition to the foregoing, because the high pressure passages are located outside of the solenoid, the size of the solenoid is necessarily limited, thereby limiting the available solenoid force.
Still further, a prior type of fuel injector utilizes a direct operated check valve, which includes upper and lower valve seats which must be precisely aligned for proper operation. Manufacturing and assembly tolerances must, therefore, be kept tight, further increasing cost.